This invention generally relates to defective NF-xcexaB activation through loss of functional NF-xcexaB Essential Modulator (NEMO). More specifically, the invention relates to diagnosis and treatment in organisms with medical conditions related to defective NF-xcexaB Essential Modulator.
Incontinentia Pigmenti (IP), or Bloch-Sulzberger Syndrome, is an X-linked dominant, male-lethal disorder with four classic cutaneous stages that begin in the neonatal period: 1) blisters and vesicles on an erythematous base; 2) raised pustular and verrucous cutaneous patches; 3) hyperpigmentation in a distinctive pattern assumed to represent lines of cell migration (lines of Blaschko); and 4) scarred dermal hypopigmentation and atrophy with absence of the hair follicles and sweat glands. The early inflammatory stages are accompanied by eosinophilia both in the peripheral blood and in the skin lesions. Streaks and whorls of hyperpigmentation give the condition its name and result from release of melanin from cells of the epidermis into the dermis, generally by 6 months of age, particularly in the axillae and groin. This xe2x80x9cmarble cakexe2x80x9d hyperpigmentation fades, typically by the third decade, leaving superficially scarred, hairless, pale tissue as the subtle dermatologic sign in adulthood. IP is often associated with developmental abnormalities of the teeth, eyes, hair, and the central nervous system (reviewed in Carney, 1976; Landy, 1993; Francis, 1997). Dental abnormalities, typically anodontia and hypodontia, conical pegging, delayed eruption, and malformed crowns with soft enamel, affect about 80% of cases (Garcia-Bravo, 1986; Optiz, 1981). Ophthalmologic anomalies, particularly dysplasia of retinal vessels, cicatrization and retinal folds, and tractional retinal detachment, affect about one-third of cases (Rosenfeld, 1985; Goldberg, 1993). Approximately 10-30% also manifest permanent neurological defects, such as intracranial vascular occlusions, neuronal remodeling or migration defects, mental retardation, hypotonia, spasticity, epilepsy, and microcephaly (Landy, 1993). IP females may also have partial or patchy alopecia even on the scalp, mild dystrophic changes in the nails, or supernumerary nipples or hypoplasia or aplasia of the breast, and show periungual keratotic tumours of the hands (Adeniran, 1993; Baran, 1998).
At birth, the ratio of female:male offspring from known affected females is consistent with lethality in utero among male conceptuses (Carney, 1976). The reasons for spontaneous male abortion (usually in the second and occasionally the third trimester) are unclear, although post mortem examination of a few cases has revealed infiltration of immune cells into tissues, indicating that IP may involve an immune response (Roberts, 1998). IP females exhibit severely skewed ( greater than 98%) X-inactivation in white blood cells and fibroblasts resulting from loss of cells expressing the mutated X (Parrish, 1996). Elimination of defective cells is likely to occur close to or immediately after birth rather than in utero in these tissues, since cell populations expressing both X-chromosomes can be derived from cord blood or from neonatal skin (Parrish, 1996). This selective mechanism may explain both the difference in morbidity between hemizygous males and heterozygous females and the gradual resolution of many of the skin signs in affected females. The cause of cell loss is unknown, although it coincides with the early inflammatory skin lesions.
Linkage of the IP locus to markers in distal Xq28 (DXS52-tel) was established with close linkage to the gene for factor VIII (Sefiani, 1989; Smahi, 1994; Parrish, 1996; Jouet, 1997) Many genes from this region have been excluded by extensive mutation screening (Heiss, 1999; Aradhya, 2000; Woffendin, 2000; Das, 1994). Recently, a gene intimately involved in inflammatory responses, NEMO/IKKxcex3, has been mapped 200 kb proximal to the factor VIII locus (Jin, 1999). NEMO is central to the activation of the ubiquitous transcription factor NF-xcexaB (Yamaoka, 1998; Rudolph, 2000). The NF-xcexaB/Rel family of transcription factors plays a particularly important role in inflammatory and immune responses, in cellular stress, and in regulating apoptosis (Ghosh, 1998; Baldwin, 1996). Their activity is induced by a variety of different stimuli including pro-inflammatory cytokines such as interleukin-1 (IL-1) and Tumour Necrosis Factor (TNF). The immediate responsiveness required of such a key regulator is effected by an unique mechanism whereby NF-xcexaB homo- or heterodimers are sequestered in the cytoplasm through interaction with an inhibitory molecule of the IKB family (three different species exist in cells: IxcexaBxcex1, IxcexaBxcex2 and IxcexaBxcex5). Upon cytokine stimulation the IxcexaB molecules are phosphorylated on two Ser residues, then polyubiquitinated and degraded through the ubiquitin-proteasome pathway. NF-xcexaB is therefore free to translocate to the nucleus and to activate its target genes. This phosphorylation event is carried out by a high molecular weight, multiprotein kinase complex containing two subunits with kinase activity (IKK1/xcex1 and IKK2/xcex2) (Zandi, 1999; Mercurio, 1999). A third component of this complex is a 48 kDa protein with no apparent catalytic activity, called NEMO (NF-xcexaB Essential Modulator), IKKxcex3, or IKKAP (Yamaoka, 1998; Rothwarf, 1998; Mercurio, 1999). NEMO directly interacts with the kinase subunits and is required for activation of the kinase complex in response to extracellular (or intracellular) stimuli: its absence results in a complete inhibition of NF-xcexaB activation.
Enhanced apoptosis might explain the selection against cells expressing the IP mutation in affected females (Smahi et al.). In support of this notion, patient-derived cell lines exhibit a high sensitivity to TNF-induced cell death. Based on these observations and the chromosomal localization of the gene in Xq28, a possible role of NEMO in IP was investigated.